Apparatus for outgassing electron tube elements



L. K. S. HAAS Dec. 17, 1968 Filed Sept. 15, 1965 M R OA T MH. V WK ATTOR/VL'V United States Patent O 3,417,278 APPARATUS FOR OUTGASSING ELECTRON TUBE ELEMENTS Laird K. S. Haas, Orefield, Pa., assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., a

corporation of New York Filed Sept. 15, 1965, Ser. No. 487,366 4 Claims. (Cl. S15-3.5)

ABSTRACT OF THE DISCLOSURE In an illustrative embodiment of the invention a conductive sleeve is slideably mounted within t-he cylindrical bore of the collector of a traveling wave tube. During evacuation, the tube is mounted collector end up so that the conductive sleeve slides down to interconnect the 'helix of the traveling wave tube with the collector. Electrical current is passed through the zhelix, the conductive sleeve and the collector to heat the helix and outgas it during the evacuation process. After evacuation, the tube is reoriented so that the sleeve drops back into the collector. The collector is then crimped to compress fand contain the sleeve permanently.

This relates to traveling wave tubes, and more particularly, -to methods and -apparatus for outgassing the slow wave structures of traveling wave tubes.

The traveling wave tube is an electron discharge device that is usually used for amplifying high frequency electromagnetic wave energy. In its usual form, it comprises an extended evacuated envelope containing -an electron gun, a slow wave structure, and lan electron collector. The slow wave structure, typically a conductive helix extending along the central axis of the envelope, amplies high frequency waves by transmitting them in proximity to an electron beam that is projected from the electron gun to the collector.

Good tube Voperation requires that the envelope be thoroughly evacuated so that the electron beam can be projected through a near-perfect vacuum. During evacuation, it is usually also the practice to outgas the conductive helix; that is, to heat the helix to drive off :any residual gases that it may contain. Tube operation subjects the helix to relatively high temperatures and a certain degree of unavoidable electron impingement. Hence, if the helix has not been previously outgassed, it will release residual gases during tube operation which may seriously interfere with the electron beam formation, projection, and focusing.

Experience rhas shown that the traveling wave tube cannot be merely heated in an external oven during evacuation because the high temperatures required for outgassing may dam-age the tube envelope, which is typically made of glass. Induction heating of the helix has been generally found to be ineffective. It is, therefore, customary to interconnect the helix and the collector with a thin wire. An electrical heating current is passed through the helix, the wire, and the collector for driving off residual gases, particularly from the helix. When these elements have been Voutgassed fat a sufficiently `high temperature, the interconnecting wire is made to disintegrate, by means of a current surge, thereby electrically isolating the collector from the slow wave structure or helix as is required for tube operation. We have found that in some instances the remnants of the disintegrated wire interfere with tube operation; for example, the remn-ants may in time contaminate the cathode surface in the electron gun.

Accordingly, it is an object of this invention to outgas elements such as a conductive helix within an electron discharge device without resort to temporary interconnect- 3,417,278 Patented Dec. 17, 1968 ice ing wires that are distintegrated and which therefore leave undesirable remnants within the device.

This and other objects of the invention are attained in an illustrative embodiment comprising a traveling wave tube having an electron gun, a conductive helix, and -a collector axially positioned within an elongated envelope. As is usual in tubes of this type, opposite ends of the conductive 'helix are connected to hollow conductive cylinders referred to as helix -matching slugs. The elements are accurately aligned so that during operation an electron beam projected from the electron gun will pass through the conductive helix to be collected within a central cylindrical bore of the collector at the opopsite end of the envelope.

1n accordance with the invention, :a hollow conductive sleeve is slideably mounted within the cylindrical bore of the collector. During evacuation, the tube is mounted collector end up so that the conductive sleeve drops down against the matching slug of the -conductive Ihelix, thereby electrically interconnecting the collector and the helix. Electrical current is passed through the helix, the conductive sleeve, and the collector to heat the helix and outgas it during the evacuation process. After evacuation has been completed, the traveling wave tube is oriented with its collector end down so that the conductive sleeve drops back into the central bore of the collector. The portion of the collector surrounding the sleeve is then crimped with a tool to contain the conductive sleeve permanently within the collector. After crimping, the collector is electrically isolated permanently from the helix as is required during tube operation. It can be appreciated that my technique -gives a desired temporary interconnection of the helix and the collector while avoiding t-he physical destruction of a temporary interconnecting wire or the like.

These and other objects -zand features of the invention will be better appreciated from a consideration of the following detailed description, taken in conjunction with the accompanying drawing in which:

FIG. 1 is a sectional view of part of a traveling wave tube at one stage of its fabrication, in accordance with the present invention;

FIG. 2 is a sectional view of part of the traveling wave tube of FIG. 1 at another stage of its fabrication', and

FIG. 3 is a sectional view of part of the traveling wave tube of FIG. 1 at still another stage of its fabrication.

Referring now to FIG. l there is shown a part of a traveling wave tube 10 at one stage of its fabrication, in accordance with the present invention. The traveling wave tube comprises an envelope 11 which contains an electron gun 12, a slow wave structure 13, and an electron collector 14. The purpose of the traveling wave tube is to transmit high frequency wave energy along the slow wave structure 13 in close proximity to an electron beam projected from a cathode 16 of the electron gun 12 toward the collector 14. During its propagation along the slow wave structure, the high frequency wave abstracts energy from the electron beam and thereby becomes amplified. In the illustrative tube shown, the slow wave structure 13 comprises a conductive helix 15, connected on opposite ends to helix matching slugs 17 and 18. As is well known in the art, the helix matching slugs are conductive cylinders of an appropriate length for giving good electromagnetic wave coupling between input and output waveguides (not shown) and the helix 15.

At one stage of the tube fabrication, the envelope 11 is evacuated by apparatus which, for purposes of clarity, has not been shown. During evacuation, it is desirable, if not essential, to heat the helix 15 to drive off any residual gases that it may contain. The most desirable way of heating the helix is to pass an electrical heating current through it because this method of heating minimizes thermal stress on the envelope 11. After fabrication, however, the collector 14 must be electrically isolated from the slow wave structure for proper operation of the device. Hence, as discussed above, one common method for heating the slow wave structure is to connect it to the collector with a thin wire so that an appropriate heating current can be passed through it. After the proper temperature has been maintained for the required outgassing time, the wire is made to disintegrate, thereby insulating the collector from the slow wave structure. This method is in some cases disadvantageous because the remnants of the destroyed wire may interfere with tube operation.

In accordance with my invention, a conductive sleeve 19 is slideably mounted within the central bore 20 of the collector 14. During evacuation, the traveling wave tube is oriented with its collector end up which causes the conductive sleeve 19 to drop down the bore 20 and abut against the helix matching slug 17 as shown in FIG. 2. The sleeve 19 is longer than the distance separating the slug 17 and the collector 14, and has a larger outside diameter than the inside diameter of the slug, so that when the sleeve drops down, the collector 14 is temporarily electrically connected with the helix 15. Hence, an appropriate heating current through the heliit 15, helix matching slug 17, sleeve 19, and collector 14, can be established by a current source 22 shown schematically in FIGS l and 2. As shown schematically in FIG. 1, the Source 22 is conveniently connected to a helix lead at one end of the tube and to a collector lead at the other end of the tube. The current heats the slow wave structure 13 to outgas it, or to drive off residual gases contained by it. These gases are, of course, evacuated from the tube by the conventional evacuation apparatus.

A peripheral recess may be provided at one end of the collector to define a relatively thin annular wall portion 24. After evacuation, the traveling wave tube is oriented with its collector end down so that the conductive sleeve 19 drops back to the bottom of the bore 20 as shown in FIG. 3. An appropriate tool is then used to crimp the wall portion 24 against the conductive sleeve 19 to permanently contain the sleeve within the end of the collector. Thereafter, during tube operation, the conductive sleeve 19 acts as part of the collector. Note that the thickness of the sleeve 19 effectively compensates for the thinness of the annular collector wall portion 24 to maintain structural strength and thermal conductivity in the collector during tube operation. The collector may, however, have a uniform wall thickness if so desired.

It can be appreciated from the foregoing that my invention is useful for temporarily interconnecting a hollow conductive member with an adjacent conductive member. As such, it could be used in traveling wave tubes having slow wave structures other than conductive helices, and indeed, could be used in electron discharge devices other than traveling wave tubes. Various modifications and embodiments other than that shown may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A traveling wave tube comprising:

a slow wave structure including at one end thereof a first conductive cylinder; an electron collector adjacent the first cylinder; a second conductive cylinder slideably mounted within the collector;

said second cylinder being longer than the distance separating the collector and the first cylinder, and having an outside diameter which is larger than the inside diameter of the first cylinder, whereby the second cylinder is adapted to interconnect the first cylinder and the collector for outgassing the tube when the traveling wave tube is oriented with its collector end up in the absence of any containing means;

and means for permanently containing the second cylinder within the collector after completion of said outgassing.

2. In an electron discharge device:

an evacuable envelope surrounding a first electrode and a second electrode;

the first electrode having a central opening and being displaced from the second electrode;

a conductive member slideably mounted within the central opening of the first electrode;

said conductive member being longer than the displacement between the first and second electrodes, whereby the conductive member is capable of temporarily electrically interconnecting the first and second electrodes in the absence of containing means;

and means for permanently and immovably containing the conductive member within the first electrode apart from the second electrode.

3. The device of claim 2 wherein:

the containing means includes a peripheral recess in the first electrode defining a wall portion that is sufficiently thin to be crimped around the conductive member.

4. A traveling wave tube comprising:

a slow wave structure including at one end thereof a first conductive cylinder;

an electron collector adjacent the first cylinder;

a second conductive cylinder slideably mounted within the collector;

said second cylinder being longer than the distance.

separating the collector and the first cylinder, and having an outside diameter which is larger than the inside diameter of the first cylinder, whereby the second cylinder is adapted to interconnect the first cylinder and the collector when the traveling wave tube is oriented with its collector end up in the absence of any containing means;

and means for permanently containing the second cylinder within the collector.

References Cited UNITED STATES PATENTS 9/1958 Iversen 315-393 X 2,947,907 8/1960 Bodrner 315-393 X 2,985,789 5/1961 St. John 315-393 X 

